1. Technical Field
The present invention relates to a technique for preventing display quality from being deteriorated when data signals whose phases are expanded are sampled.
2. Related Art
In recent years, projectors for forming a small image by using a display panel, such as a liquid crystal panel, and enlarging and projecting the small image by using an optical system have been widespread use. The projector does not have a function of forming an image, but is supplied with image data (or image signals) from a host device, such as a personal computer or a television tuner. The image data designates the gray-scale levels (brightness) of pixels, and is supplied to horizontally and vertically scan the pixels that are arranged in a matrix. Therefore, the image data is suitable for driving the display panel provided in the projector. In general, the display panel used for the projector is driven by a dot sequential method of sequentially selecting the scanning lines one-by-one, of sequentially selecting data lines one-by-one in a period where one scanning line is selected, of converting the image data into data signals suitable for driving liquid crystal, and of supplying the converted data signals to the selected data line.
Meanwhile, in recent years, there has been proposed a technique for improving the resolution of a display image. A high-resolution display image can be achieved by increasing the number of scanning lines and the number of data lines. However, in this case, since a frame frequency is fixed, the larger the number of scanning lines is, the shorter one horizontal scanning period becomes. In addition, in the dot sequential method, the larger the number of data lines becomes, the shorter the period where the data lines are selected becomes. Therefore, in the dot sequential method, it is difficult to secure sufficient time to supply the data signals to the data lines as the resolution of displayed images improves, which results in insufficient writing of the image signals onto the pixels.
Therefore, in order to solve the problem of insufficient writing, there has been suggested a phase-expansion driving method (see JP-A-2000-112437). In the phase-expansion driving method, blocks each composed of a predetermined number of data lines, for example, four data lines (six data lines in JP-A-2000-112437), are sequentially selected in one horizontal scanning period in a predetermined order, and data signals expanded four times in the time axis direction are supplied to the four data lines belonging to the selected block. In the phase-expansion driving method, it is possible to secure time required to supply the data signals to the data lines that is, for example, four times longer than that in the dot-sequential method. Thus, the phase-expansion driving method is suitable for improving the resolution of a displayed image.
Therefore, in the phase-expansion driving method, due to the data signals which are expanded four times along the time axis, the pixels arranged in every four rows corresponding to one frame have slightly different gray-scale levels, that is, strip-shaped color unevenness occurs, resulting in the deterioration of display quality.